Silver Lake IA 01-MAQ-17

Delaware County S16T88NR4W SE edge of Delhi.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

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Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:12:38 AM
Updated: 2/5/2024 8:04:35 AM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Organic Enrichment: Low Dissolved Oxygen

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2020

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as “fully supported.” The Class BLW use was assessed as “not supported” due to violations of water quality criteria for dissolved oxygen. The Class HH (fish consumption) use remains assessed as “fully supported.” Note: A TMDL for siltation and organic enrichment at Silver Lake was prepared by DNR and approved by EPA in 2002 and an additional TMDL for algae, pH, turbidity and ammonia was completed in 2008 and approved by EPA in 2009. The organic enrichment dissolved oxygen impairment is covered under the 2002 TMDL; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the current assessment/listing cycle.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2019	22280001	Silver Lake Max Depth
Iowa DNR	6	FT	See Below	1197	Silver Lake

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22280001	6	12 / 4	7.1	9.2	8.2	3	4	NO	Mon	FULL

Class A1 - Lake TSI's:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation?	Assessment Type	Support Level
22280001	6	Chlorophyll a TSI	12 / 4	26	68	58	NO	Mon	FULL
22280001	6	Secchi TSI	12 / 4	52	77	60	NO	Mon	FULL
22280001	6	Total Phosphorus TSI	12 / 4	63	82	76	NA	NA	NA
22280001	6	Fixed suspended solids	12 / 4	0.6	17	3.8	NA	NA	NA

Class BLW - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	# Acute / Chronic Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22280001	6	Dissolved Oxygen	12 / 4	3	11.4	6.9	4	NA / NA	4	YES	Mon	Not
22280001	6	pH	12 / 4	7.1	9.2	8.2	3	NA / NA	4	NO	Mon	FULL
22280001	6	Temperature	12 / 4	18.9	26.2	23.2	0	NA / NA	4	NO	Mon	FULL

Class BLW - Lake Planktonic Cyanobacteria:

Site ID	Data Source ID	# Samples	Maximum Cyanobacteria Wet Mass	Maximum Cyanobacteria % Composition	Median Cyanobacteria Wet Mass	Median Cyanobacteria % Composition	Median Cyanobacteria Concentration = 75th Percentile	Assessment Type	Support Level
22280001	6	2	0.011940004	1%	0.005970002	1%	NO	Evaluated	NA

Class BLW - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
22280001	6	Ammonia	12 / 4	0.2506	0.07	0.04	0 / 0	NO	Mon	Full

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
1197	tissue plug	2015	largemouth bass	5	29	0.05
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/18/2018

Monitoring Start

8/23/2022

Monitoring End

1/28/2002

TMDL Completed

12/15/2009

TMDL Completed

8/19/2015

Fish Tissue Monitoring

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)